Different behavioral responses to L-DOPA after anterolateral or posterolateral hypothalamic injections of 6-hydroxydopamine.

After bilateral microinjections of 6-hydroxydopamine (6-OHDA) into the anterolateral (AL) or posterolateral (PL) hypothalamus L-DOPA (1,3,4-dihydroxy-phenylalanine) produced running and rearing in AL6-OHDA rats and oral stereotypies in PL 6-OHDA rats. Since the same dose of L-DOPA had no behavioral effect in vehicle injected rats, the responses to L-DOPA of both AL and PL 6-OHDA rats are examples of behavioral supersensitivity. The different forms of behavioral supersensitivity correlated with different patterns of catecholamine (CA) denervation determined by fluorescent microscopy. The major regions of CA denervation in AL 6-OHDA rats were neocortex, hippocampus, limbic forebrain, anteromedial striatum and anterolateral hypothalamus. PL 6-OHDA had these same areas denervated and, in addition, had severe denervation of the entire striatum, parts of the amygdala and thalamus, and of the posterolateral hypothalamus. We conclude that the supersensitive behavioral response to a fixed dose of L-DOPA is determined by the pattern and/or extent of CA denervation.